Like Watergate before it, Obamacare has become the gift that keeps on giving -- to partisan opponents determined to bring down an American president.

In 1972, the Republican break-in of the Democratic National Committee headquarters at the Watergate office complex generated a seemingly endless series of stories on wrongdoing by Richard Nixon and his administration, leading to his resignation in disgrace two years later.

Now, four decades later, President Barack Obama's first-term success in enacting the health-care insurance program that popularly bears his name, after surviving a diligent Republican effort to repeal it, has fueled a similar drive to assure the failure of his presidency as well.

Seizing on the Obama administration's incredible bungling of the rollout of its crown jewel legislation, the Republican Party resurrected its fight against Obamacare and its prime political mission of discrediting the re-elected Democratic president.

Throughout Obama's first term, the Republicans in Congress marched to the unambiguous battle cry of Senate Minority Leader Mitch McConnell, who declared his prime goal was making Obama "a one-term president." In 2010, he seemed halfway home with the GOP takeover of the House, where his party effectively obstructed most of Obama's legislative agenda.

But in the 2012 presidential election, in which opposition to Obamacare was a principal Republican message to voters, the GOP stepped on its own argument. It nominated as its challenger Mitt Romney, whose own health-care insurance plan as governor of Massachusetts was a model for the Obama plan.

Although Romney insisted that his version was intended and suited for his state and not the nation, he inevitably was rendered a poor salesman for the repeal of Obamacare. For this and other reasons impairing Romney's candidacy, Obama was reelected.

After the congressional Republicans in 2013 brought about an image-tarnishing 16-day government shutdown in their failed attempt to defund Obamacare, the second-term president seemed for a time out of the woods on the issue.

But the war against Obamacare went on and has continued with renewed intensity, as its implementation has encountered a sea of logistical troubles. The program's foes suddenly had new political ammunition and determination to kill it after all.

Briefly, bipartisan compromise broke through in a budget deal that brought some hope of a more cooperative Congress. Another major Obama objective, immigration reform, now seemed possible. In light of the overwhelming Latino support for Obama in the 2012 election, many old-line Republicans argued that compromising on immigration reform was essential if the party hoped to appeal to this rising political force in 2016.

But House Speaker John Boehner has just thrown cold water on the notion, questioning whether the Obama administration "can be entrusted to enforce our laws." He spoke in the wake of the president's State of the Union notice to Congress that he would rely more on his executive-branch powers to achieve objectives blocked the legislative branch.

Boehner's retreat on immigration on grounds Obama can't be trusted reinforces the Republican focus on this president's competence and trustworthiness, made possible not only by the botched Obamacare rollout but also by his misleading assurance that citizens who liked the insurance they had could keep it.

Thus the thrust of the GOP strategy, heading into the critical midterm congressional elections and the president election beyond, is again hammering Obamacare.

Health-care reform was the president's singular legislative success in his first term, a long-sought liberal Democratic goal to go along with his party's prized social safety net achievements of Social Security and Medicare. It's ironic in the extreme that Obamacare potentially could become the undoing of his quest for a lasting presidential legacy.

Few could have imagined when the law was signed amid much jubilation at the White House in 2010 that nearly four years later, Obama would still be fighting to convince the nation that it was not a terribly divisive mistake.